Hong Kong--A sapphire and diamond ring dug out of a safe and initially appraised at less than $10,000 could sell for half a million or more at Bonhams’ May jewelry sale in Hong Kong.

Kept in a family’s bank vault after, Bonhams believes, it was purchased in the 1980s as a 30th anniversary present, the 12.92-carat sapphire ring was estimated by other auction houses to be worth $3,800 to $6,300.

But, Bonhams said, the auction houses missed a key component in assessing the piece—the center stone is a Kashmir sapphire, which is a gemstone that’s rare and collectible, especially in this size.

“Sapphires were first discovered in Kashmir around 1880, but most Kashmir mines rapidly depleted soon after,” said Graeme Thompson, Bonhams director of jewelry in Asia. “Termed as ‘blue velvet’ due to the superiority of their superb cornflower-blue hue, most Kashmir sapphires that appear on the market today were discovered more than 100 years ago.”

According to Bonhams, it was Thompson who caught the fact that the center stone might be a Kashmir and sent it to Swiss labs SSEF and Gübelin for further testing, which confirmed it was a no-heat Kashmir sapphire.

With an estimated sale price of $120,000 to $510,000, the ring is expected to lead Bonhams’ May 27 Rare Jewels and Jadeite sale in Hong Kong. The sale is comprised of 168 lots.

Aside from the Kashmir sapphire ring, the auction includes signed pieces from Harry Winston, Cartier, Van Cleef & Arpels, as well as colored gemstones and natural color diamonds.

Previews will take place in Taiwan on May 1 and 2, in Singapore from May 17 to 19, and in Hong Kong from May 23 to 26.

Click through the slideshow below to see five more pieces from the auction.

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